For first timers, I would suggest at least one "Mickey" character meal, one "Princess" character meal, at least one signature and some of WDW's more unique dining spots.
For a "Mickey" meal, our favorite is Tusker House in AK, but if you want the full Fab 5, go to Chef Mickey's (I would recommend breakfast as the food isn't great and that will be your cheapest meal option there). Also, with Chef Mickey's being at CR, you are showing them one of the original WDW resorts and, with the monorail passing through, it's WDW at its best.
For a "princess" meal, if budget allows, I would take the to CRT to get the full castle experience. If you want to save a little money, go to Akershus which is also fantastic.
For a signature meal, although Artist Point is our favorite, I would recommend Cali Grill as the view is just amazing.
For some unique dining options, consider Sci-Fi and Biergarten.
You may also want to consider HDDR. Visiting Ft. W is a lot of fun and it's a really fun show!